EMC2301 Standard Microsystems Corp., EMC2301 Datasheet - Page 18
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EMC2301
Manufacturer Part Number
EMC2301
Description
Rpm-based Pwm Fan Controller
Manufacturer
Standard Microsystems Corp.
Datasheet
1.EMC2301.pdf
(43 pages)
Available stocks
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Part Number
Manufacturer
Quantity
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Part Number:
EMC2301-1-ACZL-TR
Manufacturer:
SMSC
Quantity:
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APPLICATION NOTE: The tachometer measurement method works independently of the drive settings. If the
Revision 1.2 (03-22-10)
4.3.1
4.4
4.4.1
Programming the RPM-based Fan Speed Control Algorithm
The RPM-based Fan Speed Control Algorithm is disabled upon device power up. The following
registers control the algorithm. The EMC2301 fan control registers are pre-loaded with defaults that
will work for a wide variety of fans so only the TACH Target Register is required to set a fan speed.
The other fan control registers can be used to fine-tune the algorithm behavior based on application
requirements.
Note that steps 1 - 6 are optional and need only be performed if the default settings do not provide
the desired fan response.
1. Set the Spin Up Configuration Register to the Spin Up Level and Spin Time desired.
2. Set the Fan Step Register to the desired step size.
3. Set the Fan Minimum Drive Register to the minimum drive value that will maintain fan operation.
4. Set the Update Time and Edges options in the Fan Configuration Register.
5. Set the Valid TACH Count Register to the highest tach count that indicates the fan is spinning.
6. Set the TACH Target Register to the desired tachometer count.
7. Enable the RPM-based Fan Speed Control Algorithm by setting the EN_ALGO bit.
The tachometer measurement circuitry is used in conjunction with the RPM-based Fan Speed Control
Algorithm to update the fan driver output. Additionally, it can be used in Direct Setting mode as a
diagnostic for host based fan control.
This method monitors the TACHx signal in real time. It constantly updates the tachometer
measurement by reporting the number of clocks between a user programmed number of edges on the
TACHx signal (see
The tachometer measurement provides fast response times for the RPM-based Fan Speed Control
Algorithm and the data is presented as a count value that represents the fan RPM period.
Stalled Fan
A Stalled fan is detected if the tach counter exceeds the user-programmable Valid TACH Count setting.
If a stall is detected, the device will flag the fan as stalled and trigger an interrupt.
If the RPM-based Fan Speed Control Algorithm is enabled, the algorithm will automatically attempt to
restart the fan until it detects a valid tachometer level or is disabled.
The FAN_STALL Status bit indicates that a stalled fan was detected. This bit is checked conditionally
depending on the mode of operation.
Tachometer Measurement
Whenever the Direct Setting Mode or the Spin Up Routine is enabled, the FAN_STALL interrupt
will be masked for the duration of the programmed Spin Up Time (see
to reach a valid speed without generating unnecessary interrupts.
In Direct Setting Mode, whenever the TACH Reading Register value exceeds the Valid TACH Count
Register setting, the FAN_STALL status bit will be set.
When using the RPM-based Fan Speed Control Algorithm, the stalled fan condition is checked
whenever the Update Time is met and the fan drive setting is updated. It is not a continuous check.
Refer to
ranges (500, 1k, 2k, 4k).
device is put into Direct Setting and the fan drive is set at a level that is lower than the fan
can operate (including zero drive), then the tachometer measurement may signal a Stalled
Fan condition and assert an interrupt.
AN17.4 RPM to TACH Counts Conversion
Table
5.12).
DATASHEET
18
for examples and tables for supported RPM
RPM-Based PWM Fan Controller
Table
5.22) to allow the fan
SMSC EMC2301
Datasheet